Automatic resume from suspend for IEEE-1394 PHY

ABSTRACT

A system and process are disclosed for automatically resuming data communication using an IEEE-1394 PHY when communication is suspended because input bias is momentarily lost. The PHY determines whether data communication is suspended due to the PHY being disconnected from a network by checking the status of a connected flag. If the connected flag is still set to TRUE, the PHY was not intentionally disconnected from the network and it automatically attempts to resume communication by setting a resume flag to TRUE. The invention finds application in any type of communication device using the IEEE-1394 high-speed serial bus standard including audio and video sources, which may readily be connected to a personal computer for data storage or editing. The system and process may be implemented using software code and included within a digital signal processor (DSP).

TECHNICAL FIELD

[0001] The present invention relates generally to a system and processfor controlling a physical layer interface (PHY) in a communicationsystem, and more particularly to a system and process for automaticallyresuming communication when input bias is momentarily lost.

BACKGROUND

[0002] Electronic systems include a number of components, each of whichperforms various functions. These components must be interconnectedeither by connecting individual components together and/or by connectingthe individual components to a data bus. Various different types ofbuses have been developed depending on the type of components to beconnected and their data rates. For example, a parallel bus includesmultiple data lines allowing simultaneous transfer of multiple bits ofdata. In contrast, a serial data bus includes only a single data lineand may optionally include a clock line to ensure proper decoding ofdata.

[0003] The IEEE-1394 standard provides for a high-speed serial bus andhas been broadly adopted by the consumer electronics (CE) industry asthe single bus standard to unify communications between emergingall-digital CE devices. Due to the IEEE-1394 standard's small connectorsand serial data cables, IEEE-1394-enabled devices are consumer friendly.Furthermore, the IEEE-1394 standard's protocol supports plug-and-playoperation. As the IEEE-1394 standard becomes available on more CEdevices, such as a digital video recorder 102, a digital cable set topbox 104, a digital television 106 and an audio source 108, the devicesbeing daisy chained together as shown in FIG. 1 as part of anIEEE-1394-based network 100. These audio and video devices may beconnected to a personal computer 110, though this is not required. Thepersonal computer itself may include peripheral devices such as anexternal hard disk drive 112 and a printer 114, to which a digitalcamera 116 may be attached.

[0004] As part of the IEEE-1394 standard, which is hereby incorporatedby reference, individual devices can be placed into a suspended state toconserve energy. For example, when data is no longer required from thedigital video recorder 102, the personal computer 110 can place thedigital video recorder 102 in a suspended state. When data is laterrequired from the digital video recorder 102, the personal computer 110will send a resume command to the digital video recorder 102 and datacan once again be received from this source by the personal computer110.

[0005] For devices operating under the IEEE-1394-95 or -1394a standards,or for a device operating under the IEEE-1394b standard with a port indata strobe (D/S) mode, the loss of input bias causes the device's PHYport to transition into a suspended state. A problem arises when theloss of input bias is only momentary and not intended to transition thedevice into a suspended state.

[0006] A momentary loss of input bias that transitions the device into asuspended state has traditionally required one of two actions to resumedata communication between devices. The first action is to physicallyunplug the IEEE-1394 serial data cables between the devices. This manualintervention is undesirable and can lead to consumer dissatisfaction.Such manual intervention is especially troublesome when a number ofdevices are daisy chained together. As a consumer will not know whichlink in the daisy chain caused the problem, the consumer may be forcedto unplug and reconnect each of the IEEE-1394 serial data cables.

[0007] The second action that can cause a device in a suspended state toresume data communication requires the use of a smart controller. Insuch a system, a smart controller, a personal computer 110 for example,polls each of the devices and determines if any are unintentionally in asuspended state. If any devices are found to be in an unintentionalsuspended state, a resume command is sent. The disadvantage of thisapproach is that it requires the system to have a smart controller,which will not always be the case. For example, connecting a digitalvideo recorder 102 to a digital television 106 for playback of recordedvideotapes does not require a personal computer 110. In this case, nosmart controller is present and neither device can transmit the requiredresume command. The consumer is therefore forced to physically unplugand reconnect the IEEE-1394 serial data cable.

[0008] When a device operating in the D/S mode encounters noise spikeson the input bias, it may interpret these spikes as a command totransition into a suspended mode. The nominal input bias voltage couldbe as low as 1.165 V while the threshold voltage for detecting loss ofinput bias can be as high as 1.0 V. A voltage drop of more than 0.2 Vcan occur when new devices are connected to the daisy chained network.This is especially likely to occur due to the in-rush of currentrequired to drive the new device when the IEEE-1394 serial data cablepowers the new device. One solution to this problem is to low-passfilter the line to remove these bias drops or noise spikes. However, asnoted in the IEEE-1394a standard (see section 4.4.4), this filter musthave a relatively short time constant of 200-300 ns. Unfortunately, biasdrops and noise spikes have been observed empirically to have durationsmuch longer than this.

SUMMARY OF THE INVENTION

[0009] These and other problems are generally solved or circumvented,and technical advantages are generally achieved, by preferredembodiments of the present invention that automatically return a deviceto an active state for continued transmission of data. By automaticallyreturning the device to an active state, a consumer will avoid having tophysically unplug and reconnect each device in a network or avoid thenecessity of purchasing a smart controller and connecting each devicethereto.

[0010] In accordance with a first embodiment of the present invention, aprocess is disclosed for automatically resuming data communication at afirst physical layer interface port in an IEEE-1394 compliantcommunication system. In the process, the first physical interface portsenses a connection with a second physical layer interface port and setsa connected flag to TRUE when the connection with the second physicallayer interface port is sensed. The first physical interface port sensesan input bias and clears an input bias flag to FALSE if the input biasis not sensed. Based upon these sensing steps, the first physicalinterface port sets a resume flag to TRUE if the connected flag is TRUEand the input bias flag is FALSE. By setting the resume flag to TRUE,the first physical interface port can automatically resume datacommunication.

[0011] In accordance with a second embodiment of the present invention,a physical layer interface port in an IEEE-1394 compliant communicationsystem is disclosed that automatically resumes data communication. Thephysical layer interface port comprises two sensors and a processor. Thefirst sensor sets a connected flag to TRUE when another physical layerinterface port is sensed. The second sensor clears an input bias flag toFALSE when it does not sense an input bias. The processor, coupled toboth the first and second sensors, sets a resume flag to TRUE if theconnected flag is TRUE and the input bias flag is FALSE. The processorthereby automatically causes the physical layer interface port to resumedata communication.

[0012] In accordance with a third embodiment of the present invention, adigital signal processor (DSP) for use in a physical layer interfacecommunication port within an IEEE-1394 compliant communication system isdisclosed that automatically resumes data communication. The DSPcomprises processing code for setting a connected flag to TRUE when thephysical layer interface port senses connection with another physicallayer interface port. The processing code clears an input bias flag toFALSE when the physical layer interface port does not sense an inputbias. Lastly, the processing code sets a resume flag to TRUE if theconnected flag is TRUE and the input bias flag is FALSE. By setting theresume flag to TRUE, the processing code automatically causes thephysical layer interface port to resume data communication.

[0013] An advantage of the present invention is that it minimizes theamount of consumer interaction required to keep a network ofdaisy-chained devices operating. By automatically returning devices toan active state, the consumer is not forced to disconnect each device inthe network in an effort to find the device in a suspended state.

[0014] A further advantage of the present invention is that byautomatically returning to an active state, the consumer is not forcedto use a smart controller. As a personal computer is not needed totransfer data from the digital video recorder 102 to the digitaltelevision 106 for playback of recorded videotapes, consumer interactionand costs are reduced. Similarly, by not requiring a smart controller,two dumb devices such as the digital camera 100 and the printer 114 canbe directly connected to print a series of photographs.

[0015] The foregoing has outlined rather broadly the features andtechnical advantages of the present invention in order that the detaileddescription that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter, whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures or processes for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWING

[0016] For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings, inwhich:

[0017]FIG. 1 is an overview of a network using the IEEE-1394 high-speedserial bus standard;

[0018]FIG. 2 illustrates a two-device communication system using theIEEE-1394 standard; and

[0019]FIG. 3 illustrates the port connection state machine asimplemented by the IEEE-1394a standard.

DETAILED DESCRIPTION

[0020] A process and a system for implementing this process of thepresently preferred embodiments are discussed in detail below. It shouldbe appreciated, however, that the present invention provides manyapplicable inventive concepts that can be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the invention, and do notlimit the scope of the invention.

[0021] The present invention will be described with respect to preferredembodiments in a specific context, namely consumer electronic devices.The invention may also be applied, however, to other communicationsystems operating under the IEEE-1394 standard or other similarstandards or protocols.

[0022]FIG. 2 illustrates a simple two-device network 200 using theIEEE-1394 standard. The network comprises a first device 202 and asecond device 204 interconnected by an IEEE-1394 serial data cable 206.The first and second devices 202, 204 can correspond to devices such asthe printer 114 and the digital camera 116 (or other devices) of FIG. 1.Within the first device 202 is a link layer 208 that receives data fromcircuitry (not shown) within the first device 202 and transfers it to aPHY port 210 within the first device 202. The PHY port 210 codes thedata into the appropriate IEEE-1394 compliant serial format fortransmission over the serial data cable 206. A peer PHY port 212 withinthe second device 204 receives the data. The peer PHY port 212 thendecodes the received data and provides it to a link layer 214 within thesecond device 204 for use by the second device 204. While this processdescribes transferring data from the first device 202 to the seconddevice 204, data can similarly be transferred from the second device 204to the first device 202.

[0023] Of relevance to the present invention is the establishment ofdata transfer within the network 200 and the continued transfer of data.In particular, this data transfer may be interrupted by the possibleloss of input bias that can cause the first and/or second devices 202,204 to transition into suspended states.

[0024] The relevant state machine diagram for the active and suspendedstates within the IEEE-1394a standard is shown in FIG. 3. While thefollowing description is based upon the IEEE-1394a standard, it isapplicable to the original IEEE-1394 standard and is also applicable tothe proposed IEEE-1394b standard. The invention should also apply tosubsequent revisions to the IEEE-1394 standard as these subsequentrevisions are enacted.

[0025] Initially the first device 202 is not connected to the seconddevice 204 via the IEEE-1394 serial data cable 206 and is represented bydisconnected state P0. Upon connecting the first and second devices 202,204 together, port connection detect circuitry in the PHY port 210 ofthe first device 202 signals that the peer PHY port 212 of the seconddevice 204 has been connected. This transitions the PHY port 210 into aresuming state P1. In the resuming state P1, the PHY port 210 drives itsown output bias and tests for the presence of input bias. Assuming thePHY port 210 is connected and that input bias is present, the PHY port210 transitions to active state P2. In the active state P2, the PHY port210 is fully operational and is capable of both transmitting andreceiving data from the second device 204.

[0026] Once in the active state P2, the PHY port 210 remains in thisactive state P2 until one of three events occurs, in which case the PHYport 210 transitions into either a suspend initiator state P3 or asuspend target state P4. The first event is when the PHY port 210functions as a suspend initiator due to receiving a remote commandpacket that sets the suspend variable to TRUE in the PHY port 210. ThePHY port 210 in response transmits a remote confirmation packetacknowledging the suspend command and subsequently signals the peer PHYport 212 to suspend transmission. The PHY port 210 then transitions intothe suspend initiator state P3. The second event occurs when the PHYport 210 receives either a receive disable or a receive suspend commandthat transitions the PHY port 210 into the suspend target state P4.

[0027] The third event, and the one addressed by the present invention,occurs when the PHY port 210 detects the loss of input bias. While thisloss of input bias is usually due to unplugging the second device 204from the network 200, it may be due to noise spikes under the IEEE-1394astandard. When the PHY port detects the loss of input bias, the PHY port210 clears an input bias flag to FALSE. In this case, the PHY port 210transitions into the suspend initiator state P3.

[0028] Once the PHY port 210 is in the suspend initiator state P3, itwaits for the peer PHY port 212 to remove its bias. If the peer PHY port212 does not remove its bias within a given period, then a suspend faultflag is set to TRUE. The PHY port 210 then discharges its own outputbias and then places all of its outputs in a high impedance state.Similarly, if the PHY port 210 is in the suspend target state P4, itdischarges its output bias to acknowledge receipt of the receive suspendsignal and then places its outputs in a high impedance state. Uponputting its outputs in a high impedance state, the PHY port 210transitions into suspended state P5 from either suspend initiator stateP3 or suspend target state P4.

[0029] Once the PHY port 210 is in the suspended state P5, it generallyplaces most of the PHY port's circuitry in a low-power consumptionstate. The PHY port 210 remains in a suspended state P5 if the PHY port210 transitioned into the suspended state P5 under the fault conditionnoted above, i.e., the peer PHY port 212 did not remove the input bias.The suspend fault flag is only cleared to FALSE when the peer PHY port212 removes the input bias. Once the suspend fault flag is cleared toFALSE the PHY port 210 can transition states.

[0030] From the suspended state P5, the PHY port 210 either transitionsinto the disconnected state P0 or the resuming state P1. The PHY port210 transitions into the disconnected state P0 when it loses physicalconnection to the peer PHY port 212 as determined by the port connectiondetect circuitry that remains active even in the suspended state P5.

[0031] The PHY port 210 transitions into the resuming state P1 undereither of two circumstances under the IEEE-1394a standard. The firstoccurs when the PHY port's resume flag is TRUE. In the prior art, asmart controller would be required to set the PHY port's resume flag totrue after polling the PHY port 210 and determining that it wasunintentionally in the suspend state P5. Alternatively, if the PHY port210 detects input bias while the suspend fault flag is FALSE, the PHYport 210 again transitions into the resuming state P1. Without a smartcontroller to set the PHY port's resume flag to TRUE, the consumer facesphysically unplugging the first device 202 from the network 200, therebyforcing the PHY port 212 to reinitialize itself when the first device202 is reconnected to the network 200.

[0032] The present invention avoids the need for a separate smartcontroller or consumer intervention by having the PHY port 210automatically set the PHY port's resume flag to TRUE. Table 1 shows asubroutine from the IEEE-1394a standard for handling the suspendinitiator state P3. It should be noted that while at least two actionscan invoke this subroutine, one is most relevant to the presentinvention. The action of interest is when the PHY port 210 detects aloss of input bias and clears the input bias flag to FALSE. The otheraction that invokes this subroutine is when the PHY port 210 receives aremote command packet that sets the suspend variable to TRUE in the PHYport 210. TABLE 1 void suspend_initiator_actions() { connect_timer = 0;// Used to debounce bias or for bias handshake if (!suspend[i]) { //Unexpected loss of bias? suspend[i] = TRUE; // Insuresuspend_in_progress() returns TRUE if (child[i]) // Yes, parent stillconnected? isbr = TRUE; // Arbitrate for short reset else ibr = TRUE; //Transition to R0 for reset activate_connect_detect(i, 0); while(connected[i] && connect_timer < CONNECT_TIMEOUT / 2); // see if biaslost because of physical disconnection if (connected[i]) // A1 -- Stillconnected? resume[i] = TRUE; // A2 -- Yes, cause port to automaticallyresume. } else { // Instructed to suspend signaled = FALSE; while((connect_timer < RECEIVE_OK_HANDSHAKE) && bias[i]);  // Wait forsuspend target to deassert bias suspend_fault[i] = bias[i]; // Suspendhandshake refused by target? activate_connect_detect(i,RECEIVE_OK_HANDSHAKE); // Also guarantees handshake timing } }

[0033] The embodiment of the invention in Table 1 includes the additionof two lines of code, A1 and A2, that set the PHY port's resume flag toTRUE when the PHY port 210 and its peer PHY port 212 are stillconnected. By ensuring that the PHY port's resume flag is TRUE, thisrapidly forces the PHY port 210 to transition through the suspendedstate P5 into the resuming state P1. The code ensures the PHY port 210and its peer PHY port 212 are connected as it is undesirable for the PHYport 210 to attempt transitioning to an active state P2 when thesuspended state P5 was due to the second device 204 being disconnectedfrom the network 200 and communication is no longer possible.

[0034] Although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine, means,methods and steps described in the specification. As one of ordinaryskill in the art will readily appreciate from the disclosure of thepresent invention, processes, machines, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, means, methods, orsteps.

What is claimed is:
 1. A process for resuming data communication at afirst physical layer interface port in a communication system, theprocess at the first physical layer interface port comprising: setting aconnected flag to TRUE when a second physical layer interface port issensed; clearing an input bias flag to FALSE if an input bias is notsensed; and setting a resume flag to TRUE if the connected flag is TRUEand the input bias flag is FALSE, thereby automatically causing thefirst physical layer interface port to resume data communication.
 2. Aprocess in accordance with claim 1, wherein the communication system isan IEEE-1394 compliant communication system.
 3. A process in accordancewith claim 1, wherein the first physical layer interface port comprisesa PHY.
 4. A physical layer interface port in a communication system, thephysical layer interface port comprising: a first sensor, the firstsensor for causing a connected flag to be set to TRUE when a differentphysical layer interface port is sensed; a second sensor, the secondsensor for causing an input bias flag to be cleared to FALSE when aninput bias is not sensed; and a controller coupled to the first sensorand the second sensor, the controller for causing a resume flag to beset to TRUE if the connected flag is TRUE and the input bias flag isFALSE, the controller thereby automatically causing the physical layerinterface port to resume data communication.
 5. A physical layerinterface port in accordance with claim 4, wherein the communicationsystem is an IEEE-1394 compliant communication system.
 6. A physicallayer interface port in accordance with claim 4, wherein the physicallayer interface port comprises a PHY.
 7. A physical layer interface portin accordance with claim 4, further comprising a link layer coupled tothe controller, the link layer for transmitting data from a deviceincluding the physical layer interface port to the controller, the linklayer for receiving data from the controller and providing the data tothe device including the physical layer interface port.
 8. A physicallayer interface port in accordance with claim 4, further comprising adata communication port coupled to the controller, the datacommunication port for transmitting data to the different physical layerinterface port, the data communication port for receiving data from thedifferent physical layer interface port.
 9. A physical layer interfaceport in a communication system, the physical layer interface portcomprising: means for setting a connected flag to TRUE when a secondphysical layer interface port is sensed; means for clearing an inputbias flag to FALSE if an input bias is not sensed; and means for settinga resume flag coupled to the means for setting the connected flag, themeans for clearing the input bias, the means for setting the resume flagsetting the resume flag to TRUE if the connected flag is TRUE and theinput bias flag, thereby automatically causing the physical layerinterface port to resume data communication.
 10. A physical layerinterface port in accordance with claim 9, wherein the communicationsystem is an IEEE-1394 compliant communication system.
 11. A physicallayer interface port in accordance with claim 9, wherein the physicallayer interface port comprises a PHY.
 12. A physical layer interfaceport in accordance with claim 9, further comprising: means fortransmitting data from a device including the physical layer interfaceport to the means for setting the resume flag, the means fortransmitting data coupled to the means for setting the resume flag; andmeans for receiving data from the means for setting the resume flag andproviding the data to the device including the physical layer interface,the means for receiving data coupled to the means for setting the resumeflag.
 13. A physical layer interface port in accordance with claim 9,further comprising means for data communication coupled to the means forsetting the resume flag, the means for data communication fortransmitting data to the second physical layer interface port, the meansfor data communication for receiving data from the second physical layerinterface port.
 14. A digital signal processor for inclusion in aphysical layer interface port in a communication system, the digitalsignal processor comprising: digital signal processing code for settinga connected flag to TRUE when another physical layer interface port issensed; clearing an input bias flag to FALSE if an input bias is notsensed; and setting a resume flag to TRUE if the connected flag is TRUEand the input bias flag, thereby automatically causing the firstphysical layer interface port to resume data communication.
 15. Adigital signal processor in accordance with claim 14, wherein thecommunication system is an IEEE-1394 compliant communication system. 16.An IEEE-1394 compliant PHY comprising: a data communication port, thedata communication port for transmitting data to a different IEEE-1394compliant PHY, the data communication port for receiving data from thedifferent IEEE-1394 compliant PHY; a first sensor, the first sensor forcausing a connected flag to be set to TRUE when the different physicallayer interface port is sensed; a second sensor, the second sensor forcausing an input bias flag to be cleared to FALSE when an input bias isnot sensed; and a controller coupled to the data communication port, thefirst sensor and the second sensor, the controller for causing a resumeflag to be set to TRUE if the connected flag is TRUE and the input bias,the controller thereby automatically causing the IEEE-1394 compliant PHYto resume data communication.